1. Field of the Invention
The present invention generally relates to a method for transmitting a packet from a correspondent node to a mobile node, and more specifically, to a method for transmitting a packet from a correspondent node to a mobile node located in the same network as the correspondent node but included in a different home network than the correspondent node.
2. Discussion of the Background
A mobile internet protocol (IP) theory has been introduced to secure mobility of mobile nodes such as a notebook computer or a mobile phone that use IP to transmit data as packets between nodes. According to mobile IP theory, when different local networks are connected together through the Internet, a mobile node can move from a home network, defined as a local network to which the mobile node belongs, into an external network, defined as a local network other than the home network. When in the home network, the mobile node has a home IP address. However, when the mobile node moves into an external network, the mobile node is assigned a new IP address different than the home IP address to receive packets while in the external network.
According to the conventional method of transmitting a packet to the mobile node, the mobile node first broadcasts an agent solicitation message to locate an agent in the network where the mobile node is located. If the mobile node is located in an external network, an external agent in the external network transmits an agent advertisement message in response to the agent solicitation message. The mobile node then verifies whether the mobile node is located in the home network or whether the mobile node has moved into an external network. This step is performed by examining the external agent's IP address information included in the agent advertisement message. Thereafter, if the mobile node is located in an external network, the mobile node registers a Care of Address (COA) with a home agent in the home network to which the mobile node belongs. If the home agent receives a packet intended for the mobile node, the home agent forwards the packet to the COA in the external network. The COA is a new IP address where the mobile node receives a packet in the external network, and is substituted for the mobile node's home IP address when it has roamed into an external network. As a result, the home agent associates the home IP address with the COA of the mobile node as binding information if the mobile node moves into the external network. Therefore, when a correspondent node transmits a packet intended for the mobile node, the home agent receives the packet, detects the COA using the binding information, and routes the packet to the mobile node located in the external network.
However, according to the conventional mobile IP theory, even when the mobile node moves into an external network that is the same network as the correspondent node's local network, the mobile node's packet passes through the Internet twice. Thus, this conventional mobile IP theory is inefficient when the mobile node moves into the same local network as the correspondent node.
FIG. 1 is a diagram illustrating a conventional mobile IP theory. When a mobile node 40 moves out of a home network 300 and into an external network 100 and is treated as a mobile node 40′, the mobile node 40′ searches for a router to serve as an external agent 20. If the external agent 20 transmits a registration solicitation message from a mobile node 40′ to a home agent 30, the home agent 30 secures the connection to the mobile node 40′. Then, a correspondent node 10 transmits a packet to the home agent 30 through an Internet 200, and the home agent 30 transmits the packet to the external agent 20 through the Internet 200 based on secured binding information, such as a Foreign Agent Care of Address (FACOA). The FACOA is an IP address of the external agent 20, and when FACOA is used, all mobile nodes 40′ in an external network 100 that have home networks 300 other than the external network 100 use the FACOA as their COA.
Thus, the conventional mobile IP theory does not revise the method for transmitting a packet with the correspondent node 10 and the mobile node 40′ may be located in the same local network due to movement of the mobile node 40. As a result, when a packet is transmitted from the correspondent node 10 to the mobile node 40′ arranged in the same local network, the packet is ineffectively passed through the Internet 200, which is called “double crossing.” Although FIG. 1 shows that the mobile node 40′ receives the FACOA in the external network through the external agent 20, the double crossing is also generated when the mobile node 40′ receives a CO-LOCATED COA. When CO-LOCATED COA is used, each mobile node 40′ in an external network 100 that has a home network 300 other than the external network 100 receives a unique COA in that external network 100. Management of IP addresses to be assigned as CO-LOCATED COA in this system is usually performed by a Dynamic Host Configuration Protocol (DHCP) server, which may maintain a list of available IP addresses.
In the conventional system, when a home agent 30 receives a first packet destined for the mobile node 40′, the home agent 30 transmits updated binding information on the mobile node 40′ to the correspondent node 10. The correspondent node 10 may generate and administer the binding information on the mobile node 40′. Therefore, a method has been developed for transmitting a second packet to a mobile node 40′ in the same local network with the correspondent node 10 that does not pass through the Internet 200 based on the updated binding information transmitted in the first packet.
However, even with this method, the first packet is passed through the Internet 200 twice, or double crossed, and transmitted to the mobile node 40′. The correspondent node 10 generates and administers the binding information on the mobile node 40′ based on the updated binding information transmitted in the first packet. Therefore, there is a need for a method whereby even the first packet does not need to pass through the Internet 200.